MIMO technology (Multiple-Input Multiple-Output, multiple-input multiple-output) allows multiple antennas simultaneously transmit and receive multiple spatial streams. By using the MIMO technology, the channel capacity can be increased, in the meantime, the reliability of a channel can be improved, and the error rate can be reduced. The SDMA (Space Division Multiple Access, space division multiple access) is a newly developed multiple access technology, which use spatial segmentation to constitute different channels. Because the SDMA technology has the potential to greatly improve the capacity and performance of wireless communication systems, it has caused widespread concern from researchers.
However, when the SDMA technology is applied to the MU MIMO scenario, the coordination between users becomes a key issue. Taking a cellular network as an example, in a downlink transmission, base stations simultaneously transmit signals to users. Therefore, part of signals received by each user is inter-user interference caused by signals of other users. Although, in theory, the user can utilize multi-user detection technology to eliminate multi-user interference (Multi-User Interference, MUI), given the demand of low power consumption, low complexity and low cost of the user, the MUI is expected to be eliminated at the base station side. Under the premise that channel state information (Channel State Information, CSI) is obtained by the base station side, the inter-user interference can be eliminated by adopting the linear or non-linear pre-coding technology. However, in a MU (Multi-User, multi-user) MIMO system, in order to obtain SDMA gain, spacial multiplexing user number on a given frequency and within a given time slot is limited. In addition, if the users which are served at the same time have great spatial correlation, the transmission performance would be reduced greatly. Therefore, it is need to utilize spatial scheduling algorithms to process the user selection in SDMA, so as to maximize the transmission performance of the system.
In the present ProSched spatial scheduling algorithms, the pre-coding process is interpreted as a mapping, thereby avoiding calculating pre-coding matrixes of all of the possible combinations of users. However, the original intention of the ProSched algorithms is to be applied to a single carrier system. Although an extended method which can be applied to the multi-carrier system can also be realized, this extended method is not applicable to IEEE 802.11ac system.
There is another existing method for performing the SDMA wireless communication with at least two users simultaneously. According to that patent application, all users are pre-sequenced in accordance with a certain rule, then all possible combinations of users are generated from these pre-sequenced users, where each combination includes at least two users. In this mechanism, it is assumed that each user has only one antenna. After the base station selects all combinations of users from K user sets, where each combination of users includes U users, the base station calculates the capacity of the jth combination of users as follows. First, the base station obtains a weight vector of the jth combination of users:WZF=HH(HHH)−1=[w1w2 . . . wU]
where, WZF represents a zero-forcing weight matrix, H represents a joint channel matrix of the jth combination of users. Then, the base station obtains SNR of the uth user in the jth combination of users group with the following formula:
      SNR    u    =                                                    x            u                                    2            /                                              w            u                                    2                    σ      u      2      where, xu represents a symbol transmitted by the uth user, wu is a zero-forcing weigh vector of the uth user, σu2 is noise variance. Therefore, based on the SNR of the user, total capacity of the jth combination of users Cjtotal may be calculated according to the following formula:
      C    j    total    =            ∑              u        =        1            U        ⁢                  log        2            ⁡              (                  1          +                      SNR            u                          )            
The method uses the calculated capacity to perform scheduling.
However, the mechanism in the prior art is provide for the case that there is only one antenna at the UT side. Furthermore, the pre-coding algorithm is limited to the zero-forcing method, and how to use the scheduling mechanism and the present pre-coding algorithms jointly is not provided. When calculating the capacity according to the method, in which the zero-forcing (ZF) capacity or SNR of each combination of users is calculated and then a combination of users with the maximum ZF capacity or SNR is selected, calculating the weight matrix by adopting the zero-forcing method is introduced, however, the architecture of the MU MIMO transmission is not considered. In addition, it should be noted that the index in this method is designed only for the single carrier system or for one sub-carrier of the multi-carrier system, and could not be extended directly to be applied to the multi-carrier system.